This invention relates generally to the technical field of torque sensors and, more particularly, to a device for measuring the torque applied to a shaft.
In order to measure the torque imparted between two turning parts, elastically deforming torque meters are generally used. The deforming element frequently consists of a torsion bar. In order to prevent warp torsion and a concentration of stresses that may affect resistance to fatigue, torsion bars on torque meters are usually circular in cross section. For any given material, in isotropic linear elasticity, the angle of torsion xcex8 equals, in pure torsion:   θ  =            32      ⁢              xe2x80x83            ⁢      ML              π      ⁢              xe2x80x83            ⁢              D        4            ⁢      G      
where
D is the outer diameter of the bar, whether hollow or solid;
M is the torque applied to the torsion bar;
G is the crosswise modulus of elasticity; and
L is the working length of the bar.
Thus, given the material and geometry of a specific bar, it is possible to link the torsion angle to the torque applied to the bar.
Torsion bar torque meters are described in the following documents: FR-2 705 455, GB-2 306 641, WO-87/02319, WO-92/20560, WO-95/19557. WO-96/06330, WO-97/08527, WO-97/09221, EP-325 517, EP-369 311, EP-286,053, EP-437 437, EP-418 763, EP-453 344, EP-515 052, EP-555 987, EP-562 426, EP-566 168, EP-566 619, EP-638 791, EP-673 828, EP-681 955, EP-728 653, EP-738 647, EP-738 648, EP-765 795, EP-770 539, EP-802 107.
The primary methods for measuring the torque of a turning shaft, whether including the use of a torsion bar or not, are as follows:
methods based on electromagnetic phenomena
optical methods
electrical methods.
Magnetic methods are based essentially on the use of magnetostriction and the Hall effect.
Magnetostriction is understood to be a reversible mechanical deformation that accompanies a magnetic variation of a ferromagnetic solid. This phenomenon is reversible; that is, a deformation of a ferromagnetic material placed in a magnetic field causes a variation in magnetism (inverse magnetostriction). Examples of magnetostrictive detectors that measure torque by measuring variations in permeability of a magnetically anisotropic field are described in the following documents: EP-229 688, EP-261 980, EP-270 122, EP-288 049, EP-309 979, EP-321 662, EP-330 311, EP-338 227, EP-384 042, EP-420 136, EP-422 702, EP-444 575, EP-502 722, EP-523 025, EP-562 012, and EP-651 239.
The Hall effect is conventionally understood to be the generation of a normal magnetic field at the current density vector in a conductor or semiconductor located in a normal magnetic induction field at the current density vector. Torque sensors that operate using the Hall effect, are described in the following documents: FR-2,689,633, and FR-2,737,010.
Optical methods for measuring torque are essentially associated with interference phenomena or a measurement of optical density. Reference to these methods may be found, for example, in the following documents: EP-194 930, EP-555 987, U.S. Pat. Nos. 5,490,450, 4,676,925, 4,433,585, 5,001,937, 4,525,068, 4,939,368, 4,432,239, FR-2 735 232, FR-2 735 233, and WO-95/19557.
Electric torque measuring methods are associated essentially with capacitative measurement or measurement of a phase difference between two magnetic encoders mounted circumferentially on the torsion axis. Documents EP-263 219, EP-352 595, EP-573 808 describe devices to measure torque by extensiometric or stress gauges. Document EP-442 091 describes a mechanism to measure the angle of rotation or torque of a rotating or fixed element on a machine, which includes a torsion element in the shape of a wheel with spokes connected to various measuring devices, at least one spoke of the spoked wheel being cut so that the parts of the spoke or spokes are applied against one another after shifting caused by a predetermined bending of the other spokes. The measurement device employs Foucault currents.
The foregoing illustrates limitations known to exist in present devices and methods. Thus, it is apparent that it would be advantageous to provide an alternative directed to overcoming one or more of the limitations set forth above. Accordingly, a suitable alternative is provided including features more fully disclosed hereinafter.
In one aspect of the invention, this is accomplished by providing a device to measure torque on a turning shaft, the measuring device comprising at least one magnetic field generator placed in a first plane of a right section of the shaft, and at least one magnetic field detector placed in a second plane of a right section of the shaft. The detector produces a signal proportional to the torque producing a relative angular shift of the field generator in relation to the detector. The magnetic field generator is supported by support means connected to the turning shaft, the magnetic field detector is located roughly opposite the magnetic field generator and is supported by support means connected to the turning shaft.
The foregoing and other aspects will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawing figures.